Generalized Quadrature Space-Frequency Index Modulation System With Low-Complexity Detection

In this article, we propose a generalized quadrature space-frequency index modulation (GQSFIM) system that maps the information bits to the subcarrier activation pattern (SAP), the two antenna activation patterns (AAPs), and the modulated symbols. Specifically, two independent AAPs are utilized for the modulated symbols in a GQSFIM subblock to get higher spectral efficiency. With the help of the union bounding technique, the closed-form average bit error probability (ABEP) expression of the GQSFIM system with the maximum-likelihood (ML) detection is derived. Additionally, two low-complexity step-by-step signal detection algorithms, local ML based minimum mean-squared error (MMSE) and local ordered block based MMSE, are provided to reduce the high computational complexity of the ML detection, where the SAP, the two AAPs, and the modulated symbols are detected separately. Numerical results verify the correctness and accuracy of the theoretical ABEP of the GQSFIM system, especially in the high signal-to-noise ratio region. Moreover, the proposed GQSFIM system achieves better spectral efficiency and ABEP performance compared with the typical space-frequency index modulation systems.